~Firehawk~

iTrader: (2)

A few weeks ago I noticed my truck started making a ticking sound that sounds like an exhaust leak. First think I did was change my oil and when that didnt cure it I put in lucas oil and when that didnt help I replaced the exhaust manifold gaskets but that did not fix the problem either. Then I took it to a gm dealer and after 2 days of diagnosis they tell me its piston slap. Now I know the 5.3L engines problem with the undersized pistons and all but to me the piston slap always sounded like marbles in the engine and not like a ticking sound you would get from an exhaust leak or bad lifter.
Also I should mention that the sound can hardly be heard from on top of the engine. Instead the best place it can be heard is under the engine when I stick my head right behind the driver side wheel. But its loud enough that I hear it echoing off the cars parked on the side of the road when I drive down the street. The ticking cant really be heard at idle but instead hear best just above idle &from 750 to about 1300 RPMS
so I have (2) questions
1- can this really be piston slap making a ticking sound?
2- if its not piston slap what can it be? The kicker here is it cant really be heard from on top of the engine.
this is 2001 Silverado 5.3 with 71K on it.

Can anyone please help? Im out of ideas